1. Field of the Invention
The present invention relates to a semiconductor device and manufacturing method thereof. More particularly, the present invention relates to a technique for improving a withstanding voltage of operation of a semiconductor device while the drive capacity of the semiconductor device is being prevented from deteriorating.
2. Description of the Related Art
FIG. 10 is a cross-sectional view for explaining a conventional semiconductor device.
In FIG. 10, reference numeral 51 is a first conductive type semiconductor substrate, for example, reference numeral 51 is a P type semiconductor substrate. On the substrate 51, the gate electrode 53 is formed via the gate oxide film 52. Source drain regions of one side LDD (Lightly Doped Drain) structure are formed adjacent to the gate electrode 53. That is, on the source region side, the source region 55 of high concentration (N+ type) is formed adjacent to the gate electrode 53. On the drain region side, the drain region 54 of low concentration (Nxe2x88x92 type) is formed adjacent to the gate electrode 53, and the drain region 56 of high concentration (N+ type) is formed in the drain region 54 of low concentration. The conventional semiconductor device has the source and the drain region of one side LDD structure composed in the manner described above.
In the above semiconductor device of one side LDD structure in which a high voltage is impressed only upon the drain region side, in order to prevent an electric field from concentrating upon the drain region side, it is composed in such a manner that the drain region 56 of high concentration is surrounded by the drain region 54 of low concentration and only the source region 55 of high concentration is formed on the source region side in which a high withstanding voltage is unnecessary.
Even in the semiconductor device of the above structure, no problems are caused with respect to the static withstanding voltage. However, in the case of operation, the following problems are caused in the semiconductor device of the above structure.
The problems are described as follows. In the bipolar structure composed of a source region (emitter region), substrate (base region) and drain region (collector region), since the source region 55 of high concentration is exposed from the emitter region, the injection efficiency of carrier is high, so that the bipolar transistor is easily turned on by a low intensity of substrate electric current (I sub).
That is, since electric current gain xcex2 is high in the bipolar transistor, the withstanding voltage of drain is lowered at the operation time compared with the semiconductor device of both side LDD structure.
In this case, if a commonly used both side LDD structure is adopted, electric current gain xcex2 is lowered and it is sure that the withstanding voltage is enhanced. However, although high withstanding voltage is originally unnecessary on the source side, the common LDD structure is adopted on the source side, too. Therefore, the source side necessarily has the same length (L) of the drift region as that on the drain side. Accordingly, ON-resistance is increased and the drive capacity is lowered.
In order to solve the above problems, the first aspect of the present invention provides a semiconductor device comprising: a gate electrode formed on a first conductive type semiconductor substrate via the first and the second gate oxide film; and second conductive type sourcexe2x80xa2drain regions of low and high concentration formed adjacent to the gate electrode, wherein a diffusion region width of the sourcexe2x80xa2drain regions of low concentration on the source region side is smaller than at least that on the drain region side, and the semiconductor device further comprising a source region of high concentration formed adjacent to one end of the gate electrode; and a drain region of high concentration formed at a position distant from the other end of the gate electrode by a predetermined interval.
The first aspect of the present invention provides a method of manufacturing a semiconductor device comprising the steps of: forming a first photo resist film having a first opening in a source forming region on a first conductive type semiconductor substrate and also having a second opening, the size of which is larger than that of the first opening, in a drain forming region; forming second conductive type sourcexe2x80xa2drain regions of low concentration when a second conductive type first impurity is subjected to ion implantation into the substrate by using the first photo resist film as a mask and then the impurity is diffused; forming a element separation film in a predetermined region by selectively oxidizing while an oxidation-resistant film formed on the substrate is being used as a mask and also forming a second gate oxidation film in regions except for the element separation film and the first gate oxidation film; forming a gate electrode in such a manner that the gate electrode lies across the first and the second gate oxidation film; forming a second photo resist film having a third opening in the source region of low concentration and also having fourth opening in a region separate from the other end portion of the gate electrode in the drain region of low concentration; and forming second conductive type sourcexe2x80xa2drain regions of high concentration when ions of a second conductive type second impurity are implanted into the substrate by using the second photo resist film, gate electrode, element separation film and first gate oxidation film as a mask.
Further, the present invention provides a method of manufacturing a semiconductor device, wherein the step of forming the source-drain regions of low concentration is composed of implantation and diffusion of ions of the first impurity made of phosphorous ions, and the step of forming the source-drain regions of high concentration is composed of implantation of ions of second impurity made of arsenic ions.
Due to the foregoing, it is possible to form a source region of high concentration in the source region of low concentration so that said source region of high concentration is very close to the outer boundary of said source region of low concentration. Therefore, as compared with a structure in which the region of high concentration is formed in the region of low concentration such as an LDD structure under the condition that the drift region is separate by a distance, it is possible to enhance the withstanding voltage of drain in the case of operation while the drive capacity is being prevented from deteriorating.
The second aspect of the present invention provides a semiconductor device comprising: a gate electrode formed on a first conductive type semiconductor substrate via the first and the second gate oxide film; second conductive type source drain regions of low and high concentration formed adjacent to the gate electrode; and a first conductive type region of low concentration and a first conductive type region of high concentration formed adjacent to the source region of low concentration and the source region of high concentration.
Also, the present invention provides a method of manufacturing a semiconductor device comprising the steps of: forming a first photo resist film having an opening in the sourcexe2x80xa2drain forming regions on the first conductive type semiconductor substrate and also forming a first impurity implantation region by implanting the second conductive type first impurity into the substrate while the photo resist film is being used as a mask; forming a second photo resist film having an opening in the neighborhood of the source forming region on the substrate and also forming a second impurity implantation region by implanting the first conductive type second impurity ions into the substrate while the photo resist film is being used as a mask; forming second conductive type sourcexe2x80xa2drain regions of low concentration by diffusing the first and the second impurity and also forming a first conductive type region of low concentration adjacent to the source region of low concentration; forming a element separation film in a predetermined region by selectively oxidizing while the oxidation resistance film formed on the substrate is being used as a mask and also forming a second gate oxidation film in regions except for the element separation film and the first gate oxidation film after the first gate oxidation film has been formed; forming a gate electrode in such a manner that the gate electrode lies across the first gate oxidation film and the second gate oxidation film; forming a third photo resist film having an opening in the sourcexe2x80xa2drain forming regions of high concentration on the substrate; forming a second conductive type source region of high concentration in the source region of low concentration so that said source region of high concentration is very close to the outer boundary of said source region of low concentration and is adjacent to one end portion of the gate electrode when ions of a second conductive type third impurity are implanted into the substrate by using the third photo resist film, gate electrode, element separation film and first gate oxidation film as a mask and also forming a second conductive type drain region of high concentration in a region separate from the other end portion of the gate electrode; and forming a one-conductive region of high concentration in the region of low concentration when the first conductive type fourth impurity is subjected to ion implantation into the substrate while the fourth photo resist film is being used as a mask after the fourth photo resist film having an opening has been formed on the first conductive type region of low concentration.
Also, the present invention provides a method of manufacturing a semiconductor device, wherein the step of forming the second conductive type source drain region of low concentration and the step of forming the first conductive type region of low concentration are composed of simultaneous diffusion of the first and the second impurity, the conductive types of which are different, implanted into the substrate in the same diffusion step.
Due to the foregoing, the following effects can be provided. When the first conductive type region of high concentration is formed so that it can be adjacent to the second conductive type source region of high concentration, it becomes possible to more strongly fix the electric potential in the neighborhood of the source region, and it becomes possible to prevent the occurrence of a bipolar operation caused by the substrate electric current. Further, when the second conductive type source region of low concentration and the first conductive type region of low concentration are formed so that the second conductive type source region of high concentration and the first conductive type region of high concentration can be respectively surrounded and also when diffusion depth Xj is made equal to each other, it is possible to suppress an increase in the electric potential in the neighborhood of the source region even in a relatively deep portion of the substrate, and the electric potential can be fixed more stably.